Taiwan Patent Publication No. 399348 discloses a method for preparing a bipolar plate, which comprises: mixing at least an electrically conductive material, at least a resin, and at least a hydrophilic agent suitable for a proton exchange membrane fuel cell, to form a substantially homogeneous mixture wherein, based on the weight of said mixture, said at least an electrically conductive material is about 50% to about 95% and said at least a resin is about 5%; and molding said mixture to form a bipolar plate with a desired shape at a temperature of about 250° C. to about 500° C. and a pressure of about 500 psi to about 4000 psi, wherein said at least a resin is selected from the group consisting of thermosetting resins, thermoplastic resins, and a mixture thereof, and said at least an electrically conductive material is selected from the group consisting of graphite, carbon black, carbon fiber, and a mixture thereof.
U.S. Pat. No. 6,248,467 discloses a fuel cell composite bipolar plate, wherein the particle size of the graphite powder is mainly in the range of 80 mesh-325 mesh. This patent has mentioned that the mixing of the resin becomes inhomogeneous during processing when the particle size of the graphite powder is larger than 150 μm.
WO 00/57506 discloses a highly conductive molding composition for molding a fuel cell bipolar plate, wherein the particle size of the graphite powder used is mainly in the range of 44 μm to 150 μm, wherein the amount of the graphite powder larger than 150 μm needs to be lower than 10%, and the amount of the graphite powder smaller than 44 μm also needs to be lower than 10%.
U.S. Pat. No. 4,301,222 discloses a thin electrochemical cell separator plate with greatly improved properties made by molding and then graphitizing a mixture of preferably 50 percent high purity graphite powder and 50 percent carbonizable thermosetting phenolic resin, the graphite molding powder particles having a specified preferred shape and a size distribution requiring 31 to 62 weight percent of the particles to be less than 45 microns in size.
US patent publication No. 2005-0001352 A1 commonly assigned to the assignee of the present application discloses a composite bipolar plate of polymer electrolyte membrane fuel cells (PEMFC) prepared as follows: a) preparing a bulk molding compound (BMC) material containing a vinyl ester resin and a graphite powder, the graphite powder content of BMC material ranging from 60 wt % to 80 wt %, based on the compounded mixture; b) molding the BMC material from step a) to form a bipolar plate having a desired shape at 80-200° C. and 500-4000 psi, wherein the graphite powder is of 40 mesh-80 mesh. Details of the disclosure in US patent publication No. 2005-0001352 A1 are incorporated herein by reference.
To this date, the industry is still continuously looking for a fuel cell bipolar plate having a high electric conductivity, excellent mechanical properties, a high thermal stability and a high gas permeability-resistance.